This all works so far, and I can bring those arrays over to the QTRSensors.cpp tab with

extern int minimum_from_EEPROM[4];
extern int maximum_from_EEPROM[4];

From here I don’t know how to get the values in the array transferred into calibratedMinimumOn[i] and calibratedMaximumOn[i] in such a way that they will be used by the readCalibrated function. It needs to start out with the EEPROM values, but change to what ever values get determined by a subsequent calibration.

Since I don’t use the calibration reset, I tried changing it so that instead of resetting them to 0, it would reset the calibration to the EEPROM values.

restore_sensor(); //Read sensor calibration values out of EEPROM into minimum_from_EEPROM and maximum_from_EEPROM arrays
qtra.resetCalibration(); //Run reset function from QTRA library, but instead of setting the value to 0, set to the values in the above arrays.

This didn’t work, and in the Serial Monitor I had what looked like an error about an overflow. What can I do to get the values from my minimum_from_EEPROM[4]; and maximum_from_EEPROM[4]; arrays into the library for use with QTRA?

I suspect that your error is being caused because the calibratedMinimumOn[i] and calibratedMaximumOn[i] arrays never get allocated in the program you have that reads from EEPROM and sets those values. The description of the calibrate method in the QTR Reflectance Sensors section of the Pololu AVR Library Command Reference states that:

You can access the calibration (i.e raw max and min sensor readings) through the public member pointers calibratedMinimumOn, calibratedMaximumOn, calibratedMinimumOff, and calibratedMaximumOff. Note that these pointers will point to arrays of length numSensors, as specified in the constructor, and they will only be allocated after calibrate() has been called. If you only calibrate with the emitters on, the calibration arrays that hold the off values will not be allocated.

That guide is meant for use with our AVR libraries, rather than our Arduino library for these sensors, but they both handle the pointers the same way.

Could you try adding a call to the calibrate method before trying to write the stored maximum and minimum? If that does not work, could you try verifying that your methods to write and read EEPROM are working as you expect independently from the QTR sensor code?